| The combination of optical communication and wireless communication stands for the development direction of future communication. OFDM has been confirmed as a core technology for future wireless broadband access as well as the fourth generation mobile communication system. Thus the introduction of OFDM scheme to optical transmission network has special merits:1) Converting higher rate data stream into multiple data streams with lower rate relatively extends the symbol duration in each sub channel. In this case, high rate transmission is completed while the inter-symbol interference (ISI), caused by delay which is induced by fiber nonlinearity and chromatic dispersion, is effectively and efficiently alleviated.2) Due to the orthogonality between each other subcarriers, OFDM system could utilize the spectrum resource up to its maximum.3) Owing to the fact that IFFT as well as FFT could be adopted to implement the orthogonal modulation and demodulation in each sub channel, it is likely to implement these operations with low computational complexity.4) Because of the duration of each symbol is far longer than that of delay, complicated channel equilibrium is not required.5) OFDM system could provide robust capacity of interference cancellation, high spectrum efficiency as well as low cost of deployment and maintenance.6) OFDM is applicable to high date rate broadband communication system, simply requires equilibrium and synchronization at the receiver instead of any feedback channel, thereby simplifying the complexity of the digital signal processing (DSP).PON is a major scheme to combat the current bottleneck of optical network. The widely utilized TDM-PON requires dynamic bandwidth allocation algorithm (DBA) for time division transmission in uplink. Though WDM-PON has recently found its way in application for high transport capacity as well as high broadband for each user, its popularization is limited for its high cost. The next generation optical access network requires transporting multiple kinds of service for subscribers at the same time and new robustness and high efficient modulation techniques.OFDMA-PON dynamically allocates subcarriers to each user. OFDMA-PON could split resources synchronously in time domain and frequency domain. Compared with WDM-PON, OFDMA-PON only requires an optical receiver without multiplexing in uplink, dynamically allocates wavelengths among ONUs. In the meantime, hardware configuration is not required while adding/dropping ONU. In comparison with TDM-PON, OFDMA-PON takes advantage of multiple wavelengths transmission, thereby enabling greater capacity and farther transmission distance. It has, therefore, the following merits:1) Unique flexibility in coping with the sharing and isolating of bandwidth resource. Bandwidth could be further shared in different scenarios with distinct mode. Thus each ONU could share a single sub channel with different data rate.2) Bandwidth efficiency is improved. For instance, a10Gb/s transmission system could be realized via16QAM modulation with4bit/s/Hz within3.5GHz bandwidth.3) Transparent transmission and independent protocol. That is, the subset of subcarriers could support digital and analog signal for different QoS demand.This dissertation focuses on the key problems of the combination of OFDM techniques and PON. Chapter1briefly introduces the background and development of OFDM and optical access technology. Chapter2presents the design for coherent OFDM system diagram on the basis of DSP and frequency directly up-conversion, and elaborates signal flows and derivations of related equations. This chapter includes analysis on various PON combined with OFDM technology in current literatures, as well as analysis on polarization-multiplexing (POLMUX), source-free ONU (i.e., centralized lightwave), minimum shift keying (MSK). Chapter3firstly presents the system design and realization of the multi-P2P parallel architecture FTTH system based on isomeric8B10B coding and WDM technologies which the author has completed in earlier research on optical access network. This is followed by terminal node self-protection scheme by using unidirectional splitter-based ring. Chapter4focuses on the methodology of optimal design of OFDM system and the optimal selection on the number of subcarriers. Chapter5compares the performance between OFDMA-PON and other PON-based technologies, explores the method of system design and network topology and focuses on the failure protection mechanism of distribution fiber (DF) on the basis of the single fiber bridging connection, dual fiber bridging connection and single fiber bridging ring, which are applicable to OFDMA-PON.In this thesis, following innovative researches are introduced.Firstly, we introduced a splitter-based non-break-self-protection unidirectional ring which contains three nodes and is designed to protect the terminal nodes.The architecture, protection rules, protection switching flow and survivability analyzing in different scenes are introduced too. Calculation results showed that this proposed scheme could keep data integrity and has very high survivability and connection availability.The research works has published on SCI-indexed European Transactions on Telecommunications (ETT).Secondly, the optimal selection on the number of subcarriers of OFDM system is researched for first time. The influence on the number of subcarriers is researched from limits such as guard interval, data throughput, PAPR, operation complexity, frequency band efficiency, and sampling realizability.Thirdly, this thesis puts forward and researches on the protection of OFDMA-PON, and designs the self-protection mechanisms of DF on the basis of the single fiber bridging interconnection pair, dual fiber bridging interconnection pair and single fiber bridging interconnection ring, which are applicable to OFDMA-PON, and analyzes performance focused on the line protection and especially on the DF.Fourthly, the design and realization technologies of the point-to-point (P2P) type for fiber to the home (FTTH) system are introduced. The optical line terminal (OLT) and optical network unit (ONU) use the "aggregator and separator of audio and data" chip. Firstly the chip lets the speech signals multiplexed to the time division multiplex (TDM) E1(2.048Mb/s) signal. Then by private protocol-based8B10B coding, the El signals are converged with the100Mb/s (FE) Ethernet data signal and change to be the125Mb/s clock recover and data retiming (CDR) signal via TDM multiplexer over100Base-FX Ethernet functions. It adopts the media converting (MC) mode. It is such a single fiber wavelength-division multiplexing (WDM) bidirectional transmission system that it can transfer the video signal such as CATV with the CDR signal in same fiber. Each OLT can connect with8ONUs in the system. Each ONU can provide4E1ports, a100Mb/s port and a video signal port to the subscribers. The central network manage system can inquire real time warning signals via the bus-mastering, monitor and manage round all the units of OLT and ONU. This design realized the operation, administration and maintenance (OAM) functions which are only defined in ITU Rec.G.985simply and are not included in the traditional optical Ethernet. |
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